Free-flowing ammonium nitrate



United States Patent Ofiice 3,171,717 Patented Mar. 2, 1965 INTRODUCTION Ammonium nitrate is difficult to handle because of its tendency to cake. On storing particularly under pressure the crystals grow to greater aggregates and the product has to be crushed and often ground before use in explosives and for other purposes.

BACKGROUND nated dyestuffs which modify the crystallization process to reduce the caking. I have previously tried addition of organic compounds capable of forming micelles such as alkyl sulfate, alkyl sulfonate, alkylaryl sulfonate, or alkyl phosphate with 8-30 carbon atoms in the molecule. However, when ammonium nitrate is stored in paper bags the water arbsorbing agent may migrate to the paper causing that moisture to be more easily absorbed by the paper thus decreasing its mechanical strength.

THE INVENTION BROADLY In order to achieve a better protection I have tried to find a coating \agentcapable of a stronger binding to the nitrate. I have now succeeded in using certain organic compounds with at least one hydrophobic group and one nitrogen containing group. Treating the ammonium nitrate with these agents the nitrogen containing groups are bound to the surface of the ammonium nitrate and the hydrophobic groups will give a water repellent effect to the surface and prevent the ammonium nitrate crystals from coming in intimate contact with each other. The freeflowing and the storage properties are hence improved. The tendency to take up water and to form lumps is reduced and the lumps are readily broken down with the hand whilst an untreated ammonium nitrate after storing .becomes so hard that it has to be crushed and ground prior to use in explosive compositions.

Long-chain alkyl amines are very effective but I have found that also alkyl amides and particularly certain derivatives of hydrazine and guanidine having at least one hydrophobic group can be used for coating ammonium nitrate and other inorganic nitrates to prevent caking. To be effective the amine group has to be bound to a primary or secondary carbon atom. As to the hydrazine and guanidine derivatives this limitation does not exist and hence hydrophobic groups of various character can be introduced. These new agents are not as basic as the amines and are to be preferred over the amines in case the ammonia liberated from the ammonium nitrate by the amines causes trouble.

The improved method according to the invention for preparing an inorganic nitrate particularly ammonium nitrate of reduced tendency to cake consists in coating the crystalline nitrate with an amide, a guanidine or a hydrazine derivative having at least one hydrophobic group of at least 8 carbon atoms in a hydrocarbon group or another group of equivalent properties. The hydrophobic group may be an alkyl group, preferably of 12-20 carbon atoms, e.g., a dodecyl, hexadecyl or octadecyl group. Particularly suitable agents of the general type are octadecyl guanidine, octadecoyl carbamyl guanidine and octadecoylhydrazide.

THE AMMONIUM NITRATE The ammonium nitrate used in accordance with this invention may consist of any type of ammonium nitrate which has been heretofore used as fertilizer, in mixed fertilizers and for the manufacture of explosives. As those skilledin the art will appreciate, this comprises ammonium nitrate of a wide range of particle sizes, density, water content, etc. The exact properties of the ammonium nitrate are not critical to the present invention.

The agents of the invention may also be used as anticaking coating of sodium nitrate, calcium nitrate, mixtures containing ammonium nitrate or said nitrates.

It is most advantageous to coat the crystallized nitrate with the agent at a temperature higher than the melting point of the agent and then the nitrate is allowed to 0001 under stirring. It is possible to add the agent to a smaller part of the nitrate and then admix said portion with the bulk of the nitrate. To obtain a satisfactory effect a minimum amount of 0.001 g. of the agent has to be added for each g. of nitrate. A higher amount of the agent than 0.5 g. for each 100 g. of nitrate will not give a further improved anti-caking effect. The amount should preferably be 0.03 to 0.1 g. for. each 100 g. of the nitrate. The invention will be further described in the following illustrative, example.

Example which after cooling was kept at room temperature for two days. The specimens were then poured into small paper bags and put into a humidity oven where each 6 hours the temperature was changed from +18 to +40 C. and vice versa. The moisture content in the oven corresponded to 100% RH. (relative humidity) at +18 C., the lower temperature of the oven.

The untreated ammonium nitrate caked to a hard lump in 1-2 days. After a fortnight in the oven the degree of caking of the specimens was estimated according to a scale comprising the figures 0-5, where 0 indicates that the entire specimen had caked to a hard lump, 3 that the specimen contained smaller lumps which easily are broken down with the hand whereafter the freeflowing property of the salt was good and 5 that the specimen did not contain any lumps at all and had very good freeflowing properties. The figures of the estimation are given in the following table.

The tendency of caking was also determined in another way. 2 g. of crystalline ammonium nitrate coated with an agent listed in the table were compressed in a brass tube to cylindrical pieces with a diameter of 1.29 cm. The pressure on the surface of the specimen in the tube was varied up to l g./cm. After removal from the tube the degree of caking was determined by a crushing test,

whereby a slowly increasing pressuremaximum pressure 10 kg./cm. was applied to the test cylinders and the pressure was determined when the specimens fracture. When the test pieces fell to powder already on removal from the brass tube, the crushing pressure was indicated by the figure 0. The results obtained are given in the following table:

TABLE Estima- Crushing pressure in kgJcm. after compression in the tube attion Added aiter Compound agent. 14 days g./100 g in the 10 19 1 3s 96 115 15a 75 humidity kgJcm. g. /c1n. kgjem. kgJcm 2 kg./crn 2 kgJcm 2 lrg/cm.

oven

' -1 6. 7 7. 3 10 Octadecylarnide 0. 1 3 0 0 0 1 3. S 7. 1. 7. 3 Monooctadecyl-hydrazine 0. 1 4. 0 0 0 0 0 0 1 Do 0.05 4 O :0, 0 0 0 0 1.3

Z1 6 0.05 2 0 O 0 4.0 6.1 8.0 Monooctadecoy -hydrazide 0. 1 5 0 0 0 0 0 0 1 0. O5 4 0 0 0 0 0 0 0 3-hydroxy-2-napht'nhydrazide 0. 05 2 0 D, 0 5. 4 6. 9 7. 6 10 Octadecoyl-carbarnylguanidi 0. 1 4 0 O 0 0 0 a 0 0 o 0. O5 4 0 0 0 0 0 0 0 0ctadecoyl-carbamylguanidinesul- -l 0.1 3 0 0 0 1 5.4 7.0 10 lvlonooctadecyl-guanidine- 0. 1 4 0 0 0 0 0 0' 1 Do 0. 05 4 0 0 0 0 0 0 0 The crushing pressure of uncoated ammonium nitrate 3O 6. Ammonium nitrate coated with octadecyl hydrazide varies within broad limits depending on the way of manufacture, the moisture content and the age of the nitrate.

For coated ammonium nitrate the variations from specimen to specimen were substantially smaller. All the coated ammonium nitrate had a higher density than uncoated ammonium nitrate. This is of importance particularly for use in explosive compositions.

mens comprising ammonium nitrate coated with 0.1 g. of

any of said agents for each 100 g. of ammonium nitrate was found to dissolve at a rate of of that of the uncoated ammonium nitrate What is claimed is:

' 1. A method tor decreasing the tendency of ammonium nitrate, to cake which comprises coating crystalline ammonium nitrate with from 0.001 gram to 0.5 gram of octadecyl guanidine for each 100 grams of ammonium nitrate.

2. A method for decreasing the tendency of ammonium nitrate to cake which comprises coating crystalline ammonium nitrate with from 0.001 gram to 0.5 gram of octadecyl carbamyl guanidine for each 100 grams of'ammonium nitrate. j I

3. A method for decreasing the tendency of ammonium nitrate to calge which comprises coating crystalline ammonium nitrate with from 0.001 gram to 0.5 grain of in an amount ranging between about 0.001 and 0.5 gram per grams of ammonium nitrate.

7. A method for decreasing the caking tendencies of ammonium nitrate which consists of coating crystalline ammonium nitrate with a compound having at least one nitrogen containing group and at least one hydrophobic group, said compound being selected from the group con sisting of amides having an hydrophobic alkyl group of at least 8 carbon atoms, guanidine derivatives having an hydrophobic alkyl group of at least 8 carbon atoms and hydrazine derivatives having an hydrophobic alkyl group of at least 8 carbon atoms, said compound being present in an amount ranging between about 0.001 and 0.5 gram for each 100 grams of ammonium nitrate.

8. Ammonium nitrate coated with a compound having at least one nitrogen containing group and at least one hydrophobic group, said compound being selected from the group consisting of amides having an hydrophobic alkyl group of at least 8 carbon atoms, gnanidine derivatives having an hydrophobic alkyl group of at least 8 carbon atoms and hydrazine derivatives having an hydrophobic alkyl group of at least 8 carbon atoms, said'compound being present inan amount ranging between about 0.001 and 0.5 gram for each 100 grams of ammonium nitrate.

References Cited by the Examiner UNITED STATES PATENTS 2,616,785 11/52 Butchard 23-102 2,616,787 11/52 Whetstone 23103 2,720,446 10/55 Whetstone et al. 23-103 MAURICE A. BRt DI I. P m y am n r. 

8. AMMONIUM NITRATE COATED WITH A COMPOUND HAVING AT LEAST ONE NITROGEN CONTAINING GROUP AND AT LEAST ONE HYDROPHOBIC GROUP, SAID COMPOUND BEING SELECTED FROM THE GROUP CONSISTING OF AMIDES HAVING AN HYDROPHOBIC ALKYL GROUP OF AT LEAST 8 CARBON ATOMS, GUANIDINE DERIVATIVES HAVING AN HYDROPHOBIC ALKYL GROUP OF AT LEAST 8 CARBON ATOMS AND HYDRAZINE DERIVATIVES HAVING AN HYDROPHOBIC ALKYL GROUP OF AT LEAST 8 CARBON ATOMS, SAID COMPOUND BEING PRESENT IN AN AMOUNT RANGING BETWEEN ABOUT 0.001 AND 0.5 GRAM FOR EACH 100 GRAMS OF AMMONIUM NITRATE. 